Stabilization of polyoxymethylene with a polyesteramide and a phenolic antioxidant



United States Patent 3,355,514 STABILIZATION OF POLYOXYME'I'I IYLENEWITH A POLYESTERAMIDE AND A PHE- NOLIC ANTIOXIDANT Therese Van De Walle,Lievin, and Michel Brault, Bruayen-Artois, France, assignors toHouilleres du Bassin du Nord et du Pas-de-Calais, Douai (Nord), France,a French public establishment No Drawing. Filed Oct. 16, 1964, Ser. No.404,499 Claims priority, application France, Oct. 17, 1963, 950,859;June 12, 1964, 978,012 6 Claims. (Cl. 260857) ABSTRACT OF THE DISCLOSUREHigh molecular weight polyoxymethylene is stabilized by the addition of0.8% to by weight of a polyesteramide, and a phenolic antioxidant. In agiven example 1.5% by weight of a polyesteramide prepared from 0.75 moleof hexane diammonium adipate, 0.25 mole of adipic acid, and 0.25 mole ofethylene glycol, and 0.5% of 1,1- bis (4,2-hydroxy-5-methyl tertiarybutyl phenyl) butane was added to -a high molecular weightpolyoxymethylene.

This invention relates to the stabilisation of polyoxymethylenes againstdegradation.

Polyoxymethylenes are a group of thermoplastic resins with veryadvantageous mechanical properties containing structural units of theformula:

where n i an integer. These resins are however, subject to degradation,particularly under the influence of heat and the degradation processesmay be divided up into three different groups:

(a) Degradation of the chain ends with liberation of gaseousformaldehyde. To obviate this degradation which takes place largelyunder the influence of heat, it has been shown that the presence of anether or ester group at the end of chain prevents this degradation.

(b) Oxidation of the chains: The polyoxymethylene chains are readilyoxidisable and they may be protected from this by the addition ofanti-oxidants to the compositions. These anti-oxidants generally containphenolic or amino groups.

(c) Cleavage of the chains: The chains may cleave and then also liberateformaldehyde from the cleaved ends. To obviate this, it has beenproposed to add formaldehyde acceptors. The function of these additivesis to prevent degradation of polyoxymethylenes during its processing inthe hot state. These additives are used in conjunction with theanti-oxidants discussed above and together with ester or etherterminated chains.

Various additives have been proposed to prevent the degradation of thepolyoxymethylenes, particularly the hydrazines and their derivatives,urea, amides, such as the diamide of malonic acid, polymethacrylicamides, methyl and methacrylic amide methacrylate copolymers, andpolyamides of the type obtained by the condensation of the followingamines and acids:

"ice

1,1,6,6 tetramethylhexa-methylene diamine/adipic acid.

2,11 diaminodecane/Z-Z-S-S tetramethyladipic acid.

2,5 dimethylpiperazine/glutaric acid.

2,5 dimethylpiperazine/suberic acid.

Bis-3 aminopropylether/adipic acid.

38% polycaprolactam, 35% polyhexamethylene adipamide/27%polyhexamethylene sebacamide terpolymer.

However, these additives are not capable of being used widely unlessthey satisfy a number of conditions, viz:

The absence of toxicity.

A high insolubility in conventional solvents, more particularly Waterand stability in respect of hydrolysis.

Ease of use. In particular, an additive in an extremely divided formresults in good easy homogenisation with the polyoxymethylene powderwith little expense; and because of the good dispersion the finishedarticles tend to have no stains.

According to the present invention, we provide a thermoplasticcomposition which comprises a mixture of a polyoxymethylene and apolyesteramide. Preferably, the polyesteramide should constitute from0.8 to 5% by weight on the polyoxymethylene. These polyesteramides areexcellent formaldehyde acceptors.

The production of polyesteramides is already known per se and,particularly in the case of terephthalic polyesteramides, reference maybe made to the Journal of Polymer Science, 61 (1962), 353-359, I. L. R.Williams, Laakso and Contois L. E. The polyesteramide is formed by thereaction of a diacid with a diamine, amino acid or the correspondinglactams and a die] or aminoalcohol.

If the amount of polyesteramide usedis less than 0.8%, the maximumeffects of the polyesteramide are not obtained, and if used in excess of5%, the mechanical properties of the final polymer may be impaired.

All the polyesteramides used according to the invention may containaliphatic, aromatic or cycloalkane groups. The polyesteramides with amelting point between'120 and 230 C. are the most advantageous.

According to one aspect of the invention, the polyesteramide containsgroups derived from caprolactam. Such polyesteramides are produced byadding caprolactam to the reaction mixture from which the polyesteramideis to be obtained. These caprolactam-based polyesteramides are moreeasily dispersed and used in the polyoxymethylene, and furthermore, theyalso improve the injection and extrusion properties of the stabilisedpolyxymethylene. a

The most preferred the formula:

m p (0) {n=6 for one half of the long chain, and

n=10 for the other half, substance (e) being'a copolymer.

polyesteramides are those. having The referred polyesteramides, may beprepared by transesterifying a diester-diamide of the formula:

The lf'o'llowing reactants were heated together in a neutral atmospherein =a stainless-steel autoclave at temperatures of 270-290 C. for 2-3hours at a pressure-of '18 kg./ c'm. After which the reaction wasconcluded in vacuo (0.5 mm. Hg) for -1-2 hours and the product removedfrom the reactor. The ingredients were:

0.75 mole of'hexane diammonium adipate. 0.25 mole of adipic acid.0.25mole of ethylene glycol.

The resultant polyesteramide 'had the following .characteristics:Melting point, 220 to 222 C.; intrinsic viscositym 0.42 wasobtained.

EXAMPLE 11 Using the same procedure as in Example I, but with thefollowing ingredients:

0.65 "mole o'f-hex'an'e diammonium 'adipate. 0.35 mole-"of adipic acid.0. 3 5 mole 1- 6hexanedi0l.

A .polyesterarnide having the following characteristics: Melting point,220 C.; intrinsic viscosity 7 0.45 was obtained. 7 7

EXAMPLE Ill Using the same procedure as in Example 1, but with thefollowing ingredients:

0175 mole of hexane diammonium adipate. 0.25 mole of adipic acid. 0.25mole of "1-6 hexanediol.

:A .polyesteramide .having the following :characteristics: Meltingpoint, 220 225 C.; viscosity 1; 0.42 was obtained.

EXAMPLE IV Using the same procedure as in Example .I, but with the"fdllowing ingredients:

0.75 moleof hexane diammoniumadipate. 0.25 mole 'df'adipicacid. 0.25mole of -110 decanediol.

A polyesteramide having the following characteristics:

Melting point, 225 -'C.; viscosity 110.62 was obtained.

EXAMPLE V Using the same procedure as .in Example I, but with thefollowing ingredients:

1:1"rnole of hexane diammonium adipate.

0.54 mole'of adipic acid. 0.54 mole of ethyleneglycol. 1.1 mole of ecaprolactam.

A polyesteramide having the following characteristics: Melting point 180C.; viscosity 1 0.42 was obtained.

4 EXAMPLE VI Using the same procedure as in Example I, but with thefollowing ingredients:

0.5 mole of hexane diammonium adipate. 0.25 mole of adipic acid.

0.25 mole of 1-6 hexanediol.

0.5 mole of e caprolactam.

A po-lyesteramide having :the following characteristics: Melting point,C.; viscosity 1; 0.39 was obtained.

EXAMPLE VII Using the same procedure as in Example I, :but with thefollowing ingredients:

1.1 mole of'hexane diammonium adipate. 0.54 mole of adipic acid.

0.54 mole of 1-10 decanediol.

1.1 mole of c caprolactam.

A polyesteramide having the following characteristics: Melting point,177-180 C.; viscosity 1; 0.65 was obtained.

EXAMPLE 'VI'II Using the same procedure as in Example I, but with thefollowing ingredients:

0.25 mole of'hexane diammonium adipate. 0.25 mole of adipic acid. 0.25moleof l6 hexanediol. 1 moleof e caprolactam.

A polyesteramide having the following characteristics: Melting point 130C.; viscosity 1; 0.4 1 was obtained.

EXAMPLE IX Using the same procedure as in Example I, but with thefollowing ingredients:

0.82 mole 'of adipic acid. 0.82 mole of 1-6 hexanediol. 4.6 mole of ecaprolactam.

A polyesteramide having the following characteristics: Melting point,162l65 C.; viscosity 1; 0.45 was ob tained.

EXAMPLE X Using the same procedure as in Example I, but with thefollowing ingredients:

1.1 mole of hexane diammonium adipate. 0.54 mole of adipicacid.

0.54 mole of l.6xhexanediol.

1.1mole of s aminocaproicacid.

A polyesteramide having the following characteristics: Melting point,C.; viscosity 1; 0:48 was obtained.

EXAMPLE XI Using the same procedure as :in Example L but with thefollowing ingredients:

1.57moleof hexane diammonium adipate. 0.58 mole of adipic acid.

0.'58.mole of 1-10 decanediol.

036 mole of e aminocaproic acid.

0.25 mole of 1-4 cyclohexanedimethanol. 1 mole of e caprolactarn.

EXAMPLE XIII Using the same procedure as in Example I, but with thefollowing ingredients:

0.75 mole of hexane diammonium adipate. 0.25 mole of adipic acid. 0.25mole of 1-4 cyclohexanedimethanol.

A polyesteramide having the following characteristics: Melting point,210 C.; viscosity, 1; 0.44 was obtained.

EXAMPLE XIV Using the same procedure as in Example I, but with thefollowing ingredients:

A polyesteramide having the following characteristics: Melting point,150 C.; visocsity 1; 0.50 was obtained.

EXAMPLE XV Using the some procedure as in'Example I, but with thefollowing ingredients:

The following table shows the results with the various compoundsobtained with the polyesterarnides, produced in each of the examples.

Percent Percent Percent Percent Additive (by of loss 222 0. loss 222 0loss 222 0: Example N o.) additive after after after added min. 60 min.120 min.

Control 0 2. 7 6. 8 23 X p E l l? 8'2 5'3 5'8 xamp e Example V- g 0. :3i6 g. 38

0. Example i 2 0. 34 1. 2 5. 12 Example VII 2 3g g8 g6 5 5 Example VH1 20. s2 1. 01 4. 9 Example IX- 2 0.76 1. 9% 6. 8 --1 5' s2 1;; 1. 5 0.45 1. 57 7. 05 Example l 2 0. as 1. 49 s. 29 Example XII 2 0. 1. 3 5. 52 3-2. it? 9-2 xamp e E 1 XV f 2 0. 1. 8 7. 9 mp6 2 32* it. 3'? Examplea 01 a 1145 61s To assess the above results, the following table givesthe values obtained under the same conditions with various knownadditives.

Percent of Percent loss Percent loss Percent loss Additive additive 222C. after 222 C. after 222 C. after added 30 min. 60 min. 120 min.

Malnmmide 2 1. 2 4.1 13.1 1 Ur 2 1.3 5.1 15

Terpo1y1ner:38% polycaprolactam, 35% polyhexamethylene adipamidel27%polyhexamethylene A polyesteramide having the following characteristics:Melting point, 145 C.; viscosity, 1; 0.58 was obtained.

EXAMPLE XVI Using the same procedure as in Example I, but with thefollowing ingredients:

0.5 mole of hexane diammonium adipate. 0.25 mole of sebacic acid.

0.25 mole of 1-10 decanediol.

0.5 mole of e caprolactam.

A polyesterarnide having the following characteristics: Melting point,155 C.; viscosity 7; 0.55 was obtained.

The various polyester-amides were used for the stabilisation ofpolyoxymethylenes in various proportions.

The polyoxymethylene used in these tests was prepared by irradiation andpolymerisation of solid trioxane as described in French patentspecification No. 1,292,224 and its Additions 79,473, 79,665 and 80,142.This polyoxymethylene was then treated in accordance with the processdescribed in French patent specification No. 1,333,327. Thepolyoxymethylene thus treated has an intrinsic viscosity of 1 :06 0.5%of 1-1 bis (4,2-hydroxy-5-methyl tertiobutylphenyl) butane (aphenolic-type anti-oxidant) was then added to the composition.

T o assess the stability of the final products the resin compositionswere heated at 222 C. for /2 hour, 1 hour and 2 hours respectively andthe amount of product lost was determined at the end of each of theseperiods.

A comparison of these tables shows the superior results obtained withthe polyesteramide additives. Othertests Were carried out with certainpolyesteramides and the thermal stability of the-polyoxymethylenecompounds obtained was measured by the following test:

0.2 g. of the product undergoing test (stabilised polyoxymethylene) wasplaced in a test-tube which was then fitted in the inner casing of athermostatic jacket; this inner casing was 22 cm. long and had an insidediameter of 2.8 cm. The temperature of the jacket was set to 222 C. byboiling methyl salicylate. During the measurement the test-tubecontaining the product (length mm., outside diameter 10 mm., insidediameter 8 mm.), of Pyrex glass, was held in a vertical position insidethe jacket by a metal coil suspended from the jacket plug, its bottomend being 2 cm. above the bottom of the easing. Half an hour after thetest-tube had been fitted in the inner casing of the jacket thetest-tube was withdrawn and the loss of weight was measured. The lossper minute for 100 g. of the product was calculated and this calculatedvalue S has been given below in Examples XVII to XXI for the variousproducts under test.

The gloss of the final products obtained was also measured with aGardner Gloss Meter. This meter is specially designed for this purposeand complies with the American AS'IM Standard D 523-53 T; the gloss wasmeasured by this method at an incidence of 60 (B 60 value indicatedbelow) and an incidence of 45 (B 45 value below).

The polyoxymethylene treated in these examples was the same as thattreated in the above examples. The anti-oxidant used was 0.5% ofbis-[2-hydroxy-3-(methyl- Z-cyclohexyl)-5-met.hylphenyl] methane.

In the following examples a .polyesteramide of the fol- "lowin'g'formulawas used:

where R, m, n andp are as stated'in the examples.

EXAMPLE XVII EXAMPLE XIX Using the same treated polyoxymethylenecontaining 1.5% of a:polyesteramide'copolymerwherein: m:p=6; 71:6; 11:10(half the total quantity of glycol was used with n:6 and the other halfwith 12:10); and R .is a .para-disubstituted ,phenyl radical.

The following results were obtained: 8:003; B60: 6.3; B45:9.4.

EXAMPLE XX The same polyoxymethylene was used with an addition ofappolyesteramide obtainedby the action of the following .diesterdiam ideon ,glycol:

The melting point of "this polyesteramide was 170 C. andits'vi'scositywasOA.

The addition of 2% of this polyesteramide to the polyoxyrnethylene :gavea composition with :a loss :at 222 C. as tollows: After 30 minutes,056%,; after 60 minutes, 1.9% after LZOnninutes, 8%

'EXAMPBEJECI Using the same treated polyoxymethylene containing 1.51% ofthepolyamide formed .by'the terpolymer: 3.8% polycaprolactan, 35% Vpolyhexamethylene .adiparnide/ 27% polyhexamethylene sebacimi'de, thefollowing .results were obtained: IS:.O;03-; 360:4;9; 345:7.3.

The values for this latter example are similar to those given bycommercial polyoxym'ethylene compositions.

We claim:

1. A composition consisting essentially .of a highsmolecular weightpolyoxymethylene in admixture with a phenolic antioxidant :and apolyesteramide of the formula:

wherein m, n and p are positive integers in'the range of 1 to 12, x is apositive integer, -R and R are members of the group consisting ofalkylene radicals containing from 4 to 10 .carbon atoms and phenylene,the 'polyesterarnide being present in an amount of tromabout 0.8 toabout 5.0% by weight based on the weight of the polyoxymethylene said*ph'enolic antioxidant and polyesteramide being the sole stabilizers forthe polyoxyrrretlrylene.

2. A composition of claim 1 in which the polyesteramide has a meltingpoint of from about 120" to about 230 C.

3. .A composition of .claim 1 consisting essentially :of apolyoxymethylene and a polyesteramide containing structural unitsderived from caprola'ctam.

4. A composition of claim .1 wherein R and .R' are phenylene and m, nand p are each equal to .6.

5. A composition of claim 1 wherein 'R and R are phenylene and m and pare 6 and n is 10.

6. A composition of claim 1 wherein R and R' are phenylene and m and pare 6 and n is 6 for one half of the polycsteramide chain and 10 for theother half of the polyesteramide chain.

References Cited UNITED 'STATES PATENTS 3,235,624 2/1966 Green 260-8573,288,885

11/1966 Green 260857

1. A COMPOSITION CONSISTING ESSENTIALLY OF A HIGH MOLECULAR WEIGHTPOLYOXYMETHYLENE INADMIXTURE WIHT A PHENOLIC ANTIOXIDANT AND APOLYESTERAMIDE OF THE FORMULA: